This invention relates to diagnosis and therapy of neurodegenerative conditions.
Calcium concentrations inside nerve cells are normally tightly regulated to levels (.about.50-100 nM) several orders of magnitude lower than calcium levels in extracellular fluids (1-2 mM). Under pathological states of injury or disease, however, intraneuronal calcium concentrations increase, leading to degeneration from calcium overload (Schanne et al., Science 206:700-702, 1979). A toxic rise in calcium content stimulates a number of calcium-dependent processes, including the activation of lipases, nucleases, and proteases. The relative contributions of these various calcium-dependent enzymes to the nerve cell death triggered by calcium overload are not established, but a number of indirect studies point to the importance of activation of a calcium-dependent protease, known as calpain I or .mu.-calpain, in neurodegeneration (Siman et al., Neuron 1:279-287, 1988; Seubert et al., Brain Res. 492:366-370, 1989; Siman et al., J. Neurosci. 9:1579-1590, 1989; Siman, Neurotoxicity of Excitatory Amino Acids (Guidotti, A., ed.) Raven, New York, pp. 145-161, 1990; Lee et al., Proc. Natl. Acad. Sci. U.S.A. 88:7233-7237, 1991, and references therein).
The cytoskeleton is a mesh-like filamentous structure that maintains the structural integrity of the cell. Spectrin (also known as fodrin) is a major component of the cytoskeleton in many cell types, including neurons. Calpain-mediated proteolysis of spectrin produces a single cleavage at an identified site in the .alpha.-subunit that splits the .alpha.-subunit approximately in half (Harris et al., J. Biol. Chem. 263:15754-15761, 1988). Calpain activation and elevated levels of spectrin breakdown products (BDPs) have been associated with several neurodegenerative conditions, including those caused by Alzheimer's Disease, Parkinson's Disease, muscular dystrophy, Pick's disease, subarachnoid hemorrhage, HIV-induced neuropathy, stroke, hypoxia, ischemia, lesions, and exposure to toxins.
Lynch et al. (U.S. Pat. No. 5,118,606) describe methods for detecting cellular degeneration using antibodies to intact spectrin to detect spectrin breakdown products. Bartus et al. (WO 92/11850) describe several classes of calpain inhibitors and methods for identifying calpain inhibitors in which an antibody to intact spectrin is used in Western blot analysis to detect spectrin breakdown products.